The present invention generally relates to logical channel setting systems, and more particularly to a logical channel setting system for an asynchronous transfer mode (ATM) network.
Recently, there is active research to realize a broadband integrated services digital network (B-ISDN) using the ATM. On the other hand, a high performance parallel interface (HIPPI) has been proposed to transfer a large amount of data at a high speed between computers such as supercomputers or between a terminal and a computer. A method has also been proposed to convert HIPPI data into ATM cells at a terminal adapter (TA) on the transmitting side, to switch and transmit the ATM cells within an ATM network, and to convert the ATM cells back into the HIPPI data at a TA on the receiving side. However, in order to transmit the HIPPI data via the ATM network, it is necessary to reserve a band in which the large amount of data can be transmitted, as a virtual channel (VC, or logical channel), and the network and the like are greatly affected thereby.
FIG. 1 shows a communication system using a HIPPI interface provided by an ATM network. In FIG. 1, an ATM network 80 which is a B-ISDN is coupled to a plurality of terminal adapters (HIPPI-TA) 81 of the HIPPI interface. A HIPPI terminal equipment (TE) is coupled to each HIPPI-TA 81. In addition, the ATM network 80 is coupled to one or a plurality of terminal adapters (not shown) of other interfaces.
FIG. 2 shows the frame structure of the HIPPI protocol. As shown in line A of FIG. 2, a group of data received from a host unit, such as a computer and a TE, is called a packet, and a maximum length of this packet is 4 Gbytes. In the TE 82 of the HIPPI interface, the packet is divided into units called bursts, as shown in line B of FIG. 2, and each burst has a fixed length of 1 kbytes. The packet is transferred between the TE 82 and the HIPPI-TA 81 via parallel buses made up of a data bus, a control bus, an address bus and the like. The HIPPI-TA 81 converts the bursts into the ATM protocol. According to the ATM protocol, ATM cells having a total length of 53 octets (bytes) are generated as shown in line C of FIG. 2. Out of the 53 octets, the first 5 octets form a header and the remaining 48 octets form an information part, and the burst data are successively transmitted in division in this information part.
FIG. 3 is a diagram for explaining the HIPPI interface. As shown in FIG. 3, when making a data transfer in one direction between a HIPPI terminal (or computer) "TE" and a TA, various kinds of control signals are exchanged. Although the HIPPI interface is used for making data communication in one direction, the control signals are exchanged, that is, the control signals are transmitted in both directions. The principal signals exchanged between the transmitting side HIPPI TE 82 and a transmitting side HIPPI-TA 81 (or between a receiving side HIPPI-TA 81 and a receiving side HIPPI TE 82) include a 32-bit parallel data signal, a 4-bit parity signal with respect to the data, a request signal, a connect signal, a ready signal, a burst signal, a packet signal and the like. The request signal is ON when requesting a data transmission and becomes OFF when the data transmission ends. The connect signal indicates a state where the power source is turned ON, and the ready signal indicates that a necessary preparations are completed and the system is ready for a data transmission. The burst signal indicates the breakpoint of the burst information, and the packet signal indicates the breakpoint of the packet.
Because the HIPPI interface shown in FIG. 3 is provided between each HIPPI TE 82 and the corresponding HIPPI-TA 81, it is necessary to convert the HIPPI protocol into the ATM network protocol at the transmitting (or receiving) side HIPPI-TA 81 for transmission within the ATM network 80 and to reproduce the HIPPI protocol at the receiving (or transmitting) side HIPPI-TA 81.
Conventionally, in order to transmit normal data, a VC (FIG. 1) is set between the HIPPI-TA 81 (#1) and the other HIPPI-TA 81 (#2) at the time when a call setup request is made by the man-machine- interface (MMI) of the HIPPI-TA 81 (#1). In addition, this VC is released at the time when the disconnect request is made by the MMI of the HIPPI-TA 81 (#1).
In order to enable data transmission at the HIPPI interface, a procedure is carried out in which a request signal, which is ON, is transmitted from the transmitting side HIPPI TE 82 and a connect signal, which is ON, is returned from the receiving side HIPPI TE 82. In addition, when ending the data transmission, a procedure is carried out in which a request signal, which is OFF, is transmitted from the transmitting side HIPPI TE 82 and a connect signal, which is OFF, is returned from the receiving side HIPPI TE 82. As shown in FIG. 1, the connection of the two HIPPI TEs 82 (#1 and #2) is formed via the HIPPI-TAs 81 and the ATM network 80 in the state in which the VC is set. As described above, the VC is conventionally set at the time when the call setup request is made by the MMI of the HIPPI-TA 81, and the VC is released at the time when the disconnect request is made by the MMI of the HIPPI-TA 81.
As another example of the conventional system, there is also a system which sets the VC at a reserved time. According to such HIPPI interfaces, a broad band of 600 Mbps, for example, is declared and set to the ATM network 80 as the band which will be used when setting the VC with respect to the ATM network 80. However, after the HIPPI-TA 81 makes the call setup, responsive to the request by the MMI, there is a problem in that the VC is constantly maintained even when no data is actually transmitted from the HIPPI TE 82.
In this case, the ATM network 80 must allocate the broad band of the transmission line for the VC which is not used, and a transmission request from other HIPPI TEs 82 may not be accepted because there may not be enough margin when the available band is calculated. On the other hand, in the case where the VC is set by time reservation, the VC having the broad band is set in waste if the time in which the data is actually transmitted occupies only a short time interval of the reserved time span.